Amyloid-beta (A-beta), which exists as a 36-43 amino acid peptide, is a product released from amyloid precursor protein (APP) by the enzymes β and γ secretase. In AD patients, A-beta can be present in soluble monomers, insoluble fibrils and soluble oligomers. In monomer form, A-beta exists as a predominantly unstructured polypeptide chain. In fibril form, A-beta can aggregate into distinct morphologies, often referred to as strains. Several of these structures have been determined by solid-state NMR.
For, example, structures for several strains of fibrils are available in the Protein Data Bank (PDB), a crystallographic database of atomic resolution three dimensional structural data, including a 3-fold symmetric Aβ structure (PDB entry, 2M4J); a two-fold symmetric structure of Aβ-40 monomers (PDB entry 2LMN), and a single-chain, parallel in-register structure of Aβ-42 monomers (PDB entry 2MXU).
The structure of 2M4J is reported in Lu et al [8], and the structure of 2MXU is reported in Xiao et al [9]. The structure of 2LMN is reported in Petkova et al [10].
A-beta oligomers have been shown to kill cell lines and neurons in culture and block a critical synaptic activity that subserves memory, referred to as long term potentiation (LTP), in slice cultures and living animals.
The structure of the oligomer has not been determined to date. Moreover, NMR and other evidence indicates that the oligomer exists not in a single well-defined structure, but in a conformationally-plastic, malleable structural ensemble with limited regularity. Moreover, the concentration of toxic oligomer species is far below either that of the monomer or fibril (estimates vary but are on the order of 1000-fold below or more), making this target elusive.
Antibodies that bind A-beta have been described.
WO2009048538A2 titled USE OF ANTI-AMYLOID ANTIBODY IN OCULAR DISEASES discloses chimeric antibodies that recognize one or more binding sites on A-beta and are useful for the treatment for ocular diseases.
U.S. Pat. No. 9,221,812B2 titled COMPOUNDS FOR THE TREATMENT OF DISEASES ASSOCIATED WITH AMYLOID OR AMYLOID-LIKE PROTEINS describes pharmaceutical compositions and discontinuous antibodies that bind A-beta including an epitope between amino acid residues 12 to 24 for the treatment of amyloid-related diseases.
WO2003070760A2 titled ANTI-AMYLOID BETA ANTIBODIES AND THEIR USE discloses antibodies that recognize an A-beta discontinuous epitope, wherein the first region comprises the amino acid sequence AEFRHDSGY (SEQ ID NO: 35) or a fragment thereof and wherein the second region comprises the amino acid sequence VHHQKLVFFAEDVG (SEQ ID NO: 33) or a fragment thereof.
US20110171243A1 titled COMPOUNDS TREATING AMYLOIDOSES discloses a peptide mimotope capable of inducing the in vivo formation of antibodies that bind HQKLVF and/or HQKLVFFAED (SEQ ID NO: 16), and its use.
WO2008088983A1 and WO2001062801A2 disclose a pegylated antibody fragment that binds A-beta amino acids 13-28 (HHQKLVFFAEDVGSNK) (SEQ ID NO: 19) and its use in treating A-beta related diseases.
WO2009149487A2 titled COMPOUNDS FOR TREATING SYMPTOMS ASSOCIATED WITH PARKINSON'S DISEASE describes compounds comprising a peptide having binding capacity for an antibody specific for an A-beta epitope such as EVHHQKL (SEQ ID NO: 34), HQKLVF (SEQ ID NO: 14) and HQKLVFFAED (SEQ ID NO: 16).
The HHQK (SEQ ID NO: 1) domain is described as involved in plaque induction of neurotoxicity in human microglia, as described in Giulian D et al. [11] and Winkler et al. [12]. Non-antibody therapeutic agents that bind HHQK (SEQ ID NO: 1) have been disclosed for the treatment of protein folding diseases (US20150105344A1, WO2006125324A1).
Antibodies that preferentially or selectively bind A-beta oligomers over monomers or over fibrils or over both monomers and fibrils are desirable.